1. Field of the Disclosure
The present invention relates to a display device, more particularly, to a display device which changes a structure of an IC substrate to gain an enough step, when bonding a drive IC fabricated by using LDIC technology with a substrate of the display device made of an IC substrate and a glass substrate, and a fabricating method of the same.
2. Discussion of the Related Art
As the information age has started in earnest, a display field used to express an electrical information signal visually has been developed drastically. Together with that, a variety of flat display devices having excellent functions of slimming, reduced weights and low electricity consumption has been developed and they replace conventional cathode ray tube (CRT) devices rapidly.
Such a flat display device includes a liquid crystal display device (LCD), a plasma display panel device (PDP), a field emission display device (FED), an electro luminescence display device (ELD) and the like. They are commonly configured of a flay display panel to present images and this flat display panel has a couple of transparent insulating substrates boned with each other with a luminescent or polarizing material layer formed there between.
The liquid crystal display device (LCD) displays images by controlling light transmissivity of liquid crystal by way of an electric field. For that, the liquid crystal display device includes a liquid display panel having liquid crystal cells, a back light unit configured to emit lights to the display panel and a driving circuit configured to the liquid crystal cells.
A plurality unit pixel regions are defined and formed in the liquid crystal display panel by gate lines and data lines alternatively aligned to each other. At this time, each pixel region includes a thin film transistor array substrate, a color filter array substrate, a spacer located between the two substrates to maintain a cell gap and liquid crystal filled in the cell gap.
The thin film array substrate is configured of gate lines and data lines, a thin film transistor formed in each cross point of the gate and data lines as switch device, a pixel electrode connected with the thin film transistor with being formed in liquid crystal cell units, and an alignment layer coated thereon. The gate and data lines receive a signal from driving circuits via pad parts, respectively.
The thin transistor transmits a pixel voltage signal supplied to the data lines to the pixel electrode in response to a scan signal supplied to the gate lines.
The color filter substrate is configured of color filters formed in the liquid crystal cell units, a black matrix configured to distinguish color filters from each other and to reflect external lights, common electrodes configured to supply a reference voltage to each of the liquid crystal cells commonly and an alignment layer coated thereon.
After the thin film transistor substrate and the color filter array substrate fabricated independently as mentioned above are alignedly bonded to each other in opposite, the liquid crystal is injected and sealed.
The driving circuit of such the liquid crystal display device includes a gate driver configured to drive the gate lines of the liquid crystal panel, a data driver configured to drive the dater lines, a timing controller configured to control driving timings of the gate driver and the data driver and a power supply unit configured to supply voltage signals required to drive the driving circuits and the liquid crystal panel.
The data driver and the gate driver are divided into a plurality of integrated circuits (IC) to be fabricated as chip type.
Each of the integrated circuits is embedded in an IC region open on a tape carrier package (TCP) or embedded in a base film of TCP based on chip-on-film (COF) and it is electrically connected with the liquid crystal panel based on tape automated bonding (TAB). Also, a drive IC may be directly embedded in the liquid crystal panel based on chip on Glass (COG).
The timing controller and the power supply unit are fabricated as chip type and they are embedded on a main printed circuit board (PCB).
As follows, a pad part forming method of a conventional liquid crystal display device will be described in reference to the accompanying drawings.
FIGS. 1A to 1F are process sectional views illustrating the pad part forming method of the conventional liquid crystal display device.
As shown in FIG. 1A, a pad metal 11 is formed on a pad part 10 of a lower substrate including the thin transistor array.
As shown in FIG. 1B, a conductive adhesive 20 is opposed to a surface having the pad metal 11 formed therein and a pressing device 30 applies weak pressure and heat to the surface and the conductive adhesives 20 to implement pre-bonding. At this time, a protection film 21 is attached to a surface of the pressing device 30 in contact with the conductive adhesive 20 and the protection film 21 is detached from the conductive adhesive 20 in a process shown in FIG. 1C.
As shown in FIG. 1D, a semiconductor IC 40 having a bump 41 is opposed on a substrate 10 having the conductive adhesive 20 placed thereon. In this case, the conductive adhesive 20 faces the bump 41. This bump may be made of metal material such as Nickel, Copper and the like and it has a height of n-μm.
As shown in FIG. 1E, stronger pressure and heat than the pressure and heat in the process of FIG. 1B may be applied to the semiconductor IC 40 by using the pressing device 30 and a bonding process is implemented. In this process, the pressure is transmitted to bond a connection pad terminal 41 of the IC substrate 40 with a pad metal 11 placed on the substrate 10, and the pressed conductive adhesive 20 remains in the other area.
Here, not shown in the drawings, the conductive adhesive 20 includes a conductive ball and adhesive material. The conductive ball remains between the bump 41 of the metal material and the pad metal 11 to create electrical contact and the adhesive material is used as adhesive in the other area.
According to a conventional pad part formation process, bonding is implemented by using PCP (Tape Carrier Package) or COF (Chip On Film) having the typical semiconductor IC mounted therein. In case of the semiconductor IC, conductive adhesive having quite a thickness is used in the bonding process to gain a step required in the bonding process.
In the meanwhile, recently, LDIC (Low Temperature Poly Silicon Driver Integrated Circuit) technology has been under development. According to the LDIC, a drive IC is formed on a glass substrate based on LTPS (Low Temperature Poly Silicon) and the drive IC is attached to a liquid crystal panel.
However, when the substrate having the drive IC mounted therein is attached to a lower substrate of the liquid crystal panel, uniformity of the pad part cannot be accomplished, with weak contact.